A surface-mounted resistor to be mounted on a surface-mounted substrate is generally used in, e.g., a vehicle. For example, Patent Document 1 (Japanese Laid-Open Patent Publication No. (Hei) 7-201507) discloses a chip resistor that has been proposed by the applicants of the present disclosure. As described in paragraph [0002] of Patent Document 1, vehicle electronic components are required to be capable of withstanding high voltages.
Patent Document 2 (Japanese Laid-Open Patent Publication No. (Hei) 8-203701) discloses a chip-type fixed resistor used in a circuit such as a vehicle electronic component, to which a surge voltage is applied. More particularly, Patent Document 2 provides a chip-type fixed resistor having an improved surge withstanding property that suppresses discharge between electrodes. As shown in FIG. 2 of Patent Document 2, a pair of lateral electrodes covering a part of an upper surface electrode is provided on a lateral surface of an alumina substrate.
Patent Document 3 (Japanese Laid-Open Patent Publication No. (Hei) 11-68284) discloses a surface-mounted electronic component for restraining fatigue, cracks, and breaks due to thermal stress that is generated at a solder fillet tip and a solder joint. For such property, recesses and protrusions are provided on an electrode that is disposed on both lateral surfaces of the surface-mounted electronic component. In this way, stress concentration may be alleviated.
Patent Document 4 (Japanese Laid-Open Patent Publication No. (Hei) 7-230901), which has been filed by the applicants of the present disclosure, discloses a surface-mounted type electronic component for alleviating impact applied to a lead terminal in the process of being mounted on a surface-mounted substrate. For this purpose, the surface-mounted type electronic component is mounted on the surface-mounted substrate by interposing a buffer member therebetween.
Patent Document 5 (Japanese Laid-Open Patent Publication No. (Hei) 8-115803) discloses a chip resistance component that is surface-mountable on a printed wiring board. More particularly, Patent Document 5 describes that a soldering section of the chip resistance component is not cracked or peeled upon being mounted. As described in paragraph [0007] and shown in FIGS. 1(a) through 1(c) of Patent Document 5, a hole 16 is provided in a vertical portion 15a so as to strengthen a connection between an external electrode 15 and a resistance element 10. Also, with reference to FIG. 5 of Patent Document 5, an external electrode 45 is made up of a vertical portion 45a, a lower portion 45b, a lateral portion 45c, and an upper portion 45d. As shown in FIG. 5 of Patent Document 5, the external electrode 45 is attached on both ends of the resistance element 10 by burying the lateral portion 45c through an insert molding. Further, surfaces of the vertical portion 45a, the lower portion 45b, and the upper portion 45d are aligned on the same level as a surface of the resistance element 10, thereby being exposed to the outside.
Patent Document 6 (Japanese Laid-Open Patent Publication No. 2001-297942) discloses an electronic component provided with terminals. The electronic component has durability against stress applied from a circuit board in the process of being mounted on the circuit board by soldering. Also, the terminals of the electronic component are configured in a flat structure (i.e., a low height structure) that restrains problems caused by the insufficiency and suction of a solder in the mounting process.
Patent Document 7 (Japanese Laid-Open Patent Publication No. 2002-325302) discloses an apparatus and a method for accurately detecting an electric leakage occurring in a power supply that supplies electric power to a motor used in an electric motor vehicle such as a hybrid car, an electric automobile, and the like. As described in paragraph [0002] of Patent Document 7, an output voltage of the power supply employed in the electric motor vehicle is significantly high, e.g., 200 Volts (V) or more, such that an electric leakage in the power supply may cause significant damage. To address this problem, for the safety in a vehicle electronic system, the power supply should not be directly grounded and a leakage resistance should be detected so as to prevent the electric leakage. The leakage resistance refers to a resistance between the power supply and ground. Therefore, this leakage resistance may be detected by connecting the power supply to ground through a ground resistor of an electric leakage detection circuit. Considering the above, the ground resistor is required to have as large a resistance value as possible so as to prevent the risk of electrical shocks.
FIG. 11 shows a cross-sectional view illustrating a configuration of a surface-mounted resistor that is mounted on a surface-mounted substrate. A surface-mounted resistor 900 includes a flat-type base member 902, a resistance element 904, a protective film 906, a pair of upper electrodes 908, a pair of lateral electrodes 910, and a pair of lower electrodes 912.
The lateral electrodes 910 and the lower electrodes 912 of the surface-mounted resistor 900 are mounted on pads 918 of a surface-mounted substrate 916 by interposing solder fillets 920 therebetween.
Referring to FIG. 12, a partial schematic cross-sectional view illustrating a crack generated in the solder fillet 920 when the surface-mounted resistor 900 (as shown in FIG. 11) is being mounted on the surface-mounted substrate 916 is shown. The material of the flat-type base member 902 such as alumina has a different coefficient of linear thermal expansion from the material of the surface-mounted substrate 916 (serving as an insulation substrate) such as glass epoxy. For this reason, repetitive variations in the temperature in the above structure, where the surface-mounted resistor 900 is mounted on the surface-mounted substrate 916, may cause a shear force to be applied to the solder fillet 920, which in turn causes a crack K thereon.
FIG. 13 shows a schematic cross-sectional view illustrating an electronic component with a pair of L-shaped terminals, which is mounted on a surface-mounted substrate. The electronic component shown in FIG. 13 is a partial variation of the electronic component having electrodes shown in FIG. 9 of Patent Document 6. An electronic component 950 having a pair of L-shaped terminals is provided with an electronic element 952, a pair of internal electrodes 954, a pair of conductive resins 956, and a pair of external electrodes 958.
Each of the external electrodes 958 is provided with a stress alleviation portion 958a. The electronic component 950 is mounted on an insulation substrate 962 by interposing solder fillets 960 therebetween.
The electronic component 950 shown in FIG. 13 is provided with the electronic element 952 and the pair of internal electrodes 954. The electronic element 952 is configured to be mounted on the insulation substrate 962 through the pair of external electrodes 958, such that the stress alleviation portions 958a alleviate shear force applied to the solder fillets 960, thereby preventing the generation of cracks.
The external electrodes 958 and the internal electrodes 954 are fixed to each other by the conductive resins 956 in a direction perpendicular to the insulation substrate 962. However, in this structure, if the electronic component 950 having these electrodes is configured in a flat structure, it may be difficult to secure a large fixation area in a vertical direction. Therefore, there may be a problem that the fixation area between the external electrode 958 and the internal electrode 954 becomes insufficient.
Also, the movement of the stress alleviation portion 958a is limited by the solder fillet 960 formed along the external electrode 958, such that the shear force possibly being applied to the solder fillet 960 may not be sufficiently absorbed by the stress alleviation portion 958a. 
Patent Document 1 describes the object of suppressing the deterioration of a surge voltage withstanding property. However, Patent Document 1 merely discloses the structural feature of a chip resistor while it neither suggests nor teaches mounting the chip resistor on the surface-mounted substrate.
Patent Document 2 proposes substantially the same object as Patent Document 1, for suppressing the deterioration of a surge voltage withstanding property. Therefore, Patent Document 2 suggests a rounding treatment on angled portions of both ends of electrodes of the chip resistor. However, Patent Document 2 neither suggests nor teaches possible problems that may be caused during a chip resistor mounting process, and countermeasures for such problems.
Patent Document 3 discloses the surface-mounted electronic component and considers problems such as fatigue, cracks, and breaks due to thermal stress generated at the solder fillet tip and the solder joint. For overcoming the problems, Patent Document 3 suggests that the recesses and protrusions should be provided on the electrodes so as to absorb stresses. Unfortunately, this approach may cause another problem that such electrode structure requires a more complicated manufacturing process resulting in a high manufacturing cost.
Patent Document 4 considers stress that is generated on the electronic component in the process of being mounted on the surface-mounted substrate. For alleviating such stress, Patent Document 4 discloses that the buffer member is formed between a lower surface of the electronic component and the surface-mounted substrate. As described in Patent Document 4, a resin material such as an expanded urethane, a silicone resin and the like, and a rubber material such as a silicone rubber are used as the buffer member. However, in order to precisely control a thickness and an application range of the buffer member, a more complicated manufacturing process and apparatus is necessary, which increases manufacturing cost. Therefore, such approach may not be preferable.
Patent Document 5 discloses the chip resistor component that is surface-mountable on a printed wiring board. As shown in FIG. 5 of Patent Document 5, the external electrode 45 may be similar in shape to an E-shaped external electrode in accordance with one embodiment of the present disclosure. However, the external electrode 45 is configured to be buried through the insert molding, which is structurally different from the external electrode of the present disclosure. Such difference will be apparent from the following descriptions.
Patent Document 6 considers alleviating stress due to thermal expansion and contraction in the circuit substrate. However, as described in Patent Document 6, the external electrodes are disposed on both lateral surfaces of the electronic component.
Patent Document 7 discloses, in paragraph [0018], that the risk of electric shocks is decreased by employing a voltage-dividing resistor in the electric leakage detection apparatus, the voltage-dividing resistor having a large resistance value, for example, 1 to 10 Mega Ohms. However, Patent Document 7 neither suggests nor teaches the structure of a surface-mounted resistor having a large resistance value.